Thermoplastic molding compositions containing polycarbonate, graft polymer, and polyalkylene terephthalate are known. Many such compositions have been disclosed in the patent literature. Mention may be made in this context of U.S. Pat. No. 4,888,388 which disclosed an impact resistant thermoplastic composition having distinguished surface appearance, color stability and thermal stability. The composition contains a particular graft rubber copolymer, polycarbonate and saturated polyester. A self extinguishing polycarbonate composition, stabilized against degradation and containing a halogenated phosphorous compound has been disclosed in U.S. Pat. No. 3,557,053. Also known are compositions which contain phosphorous compounds as additives, primarily as flame retarding agents. The combination of phosphorous compounds with halogenated additives has been disclosed to impart flame resistance to thermoplastic compositions. U.S. Pat. No. 5,276,077 is noted in this connection for its disclosure of an ignition resistant composition which contains polycarbonate, rubber modified monovinylidene aromatic copolymer and a rubbery core/shell graft copolymer impact modifier.
Also relevant in the present context are the following articles:
1. Flame Retarding Polybutylene Terephthalate--properties, processing characteristics and Rheology, by J. Green and J. Chung, Journal of Fire Sciences, Vol 8 --Jul./Aug. 1990, and PA0 2. Flame Retarding Engineering Thermoplastics with Brominated Phosphate Esters, by J. Green, Proceedings of Sixteenth International Conference on Fire Safety, Jan. 14, 1991, Millbrae, Calif., and PA0 3. Flame Retarding Polycarbonate/ABS Blends With a Brominated Phosphate, by J. Green, presented at the Fire Retardant Chemicals Association Meeting, Hilton Head, Mar. 20, 1991.